Influence of cooling method on tensile properties and damage constitutive model of layered sandstone after high temperature

To study the influence of different cooling methods on the stability of high temperature layered tunnel surrounding rock after fire condition, the direct tensile test after natural cooling and water cooling was carried out with Sichuan sandstone as the research object. The change rules of tensile strength and elastic modulus of square layered sandstone under direct tensile test was studied, and the influence of cooling method on the failure of three-dimensional morphology of layered sandstone was also analyzed. The statistical damage constitutive model of layered sandstone under tensile action is established based on the statistical damage principle and the damage threshold is introduced, which is verified with the experimental data. The results show that the elastic modulus and tensile strength of rocks with different bedding angles show obvious anisotropy, and they all show a V-shaped trend. At the same bedding angle, water cooling causes more serious damage to rocks than natural cooling. Tthe height differences of different bedding angles (0°, 30°, 45°, 60°, 90°) are 1.802mm, 3.254mm, 4.868mm, 3.047mm, and 1.758mm, respectively. Additionally, it is suggested that the calculated values of the statistical damage constitutive model fit well with the experimental values, and the model parameters m and F₀ are related to the macroscopic elastic modulus and strength. This has a certain theoretical value for analyzing the evaluation of the stability of tunnel surrounding rock after high temperature under fire condition.